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25 lines
602 B
Markdown
25 lines
602 B
Markdown
---
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date: 20201109
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id: d1549dd2-a5fc-4583-a186-5de02ca40d33
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title: JavaScript Lookbehind Assertions
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---
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# Examples
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## Positive lookbehind assertion
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Text preceding the current location must match the assertion
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``` javascript
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const RE_DOLLAR_PREFIX = /(?<=\$)foo/g;
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console.log("$foo %foo foo".replace(RE_DOLLAR_PREFIX, "bar")); // '$bar %foo foo'
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```
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## Negative lookbehind assertion
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Text preceding the current location must not match the assertion
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``` javascript
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const RE_NO_DOLLAR_PREFIX = /(?<!\$)foo/g;
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console.log("$foo %foo foo".replace(RE_NO_DOLLAR_PREFIX, "bar")); // '$foo %bar bar'
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```
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